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Dental Materials > Composites > Flashcards

Composites Flashcards

1
Q

What is a Composite?

A

A solid with 2 or more distinct constituent materials or phases(enamel, bone, dentin and reinforced polymers all qualify)

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2
Q

Composite is normally referred to as:

A

reinforced polymer system used for restoring hard tissues

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3
Q

What are the 4 components of a composite?

A
  1. organic polymer matrix
  2. Inorganic filler particles
  3. Coupling agent
  4. Initiator-accelerator system
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4
Q

What usually makes up the organic polymer matrix?

A

Bis-GMA, UDMA or Silorane-new low-shrinkage monomer

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5
Q

4 types of inorganic filler particles

A
  1. quartz or glass
  2. sol-gel derived ceramics
  3. microfine silica
  4. nanoparticles
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6
Q

What is the biggest component of a composite by weight

A

Inorganic filler particles

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7
Q

What do inorganic filler particles provide for composite

A
  1. translucency

2. reduces shrinkage 3.reinforces resin matrix

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8
Q

What does a coupling agent do?

A

forms a bond between inorganic filler particles and organic resin matrix. Also makes hydrophobic and enhances mechanical properies
-silane is most common

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9
Q

What does the initiator-accelerator system do?

A

polymerize and cross-links system into a hardened mass Ex:camphorquinone absorbs blue light

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10
Q

Purpose of composites

A

esthetics, high stress areas. (they have lower wear and lower expansion than acrylics and silica)

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11
Q

Composites are classified by:

A
  1. Shape
  2. particle size
  3. Particle distribution of the filler
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12
Q

Are nano hybrids a true nanofill?

A

no because they are mixed with bigger chunks

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13
Q

Nanofills particle size

A

1-100 nm

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14
Q

Camphorquinone

A

absorbs blue light and starts curing process

is an initiator-accelerator

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15
Q

how are composites polymerized

A

free radical addition polymerization of methacrylate monomers

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16
Q

Stages of polymerization

A
  1. intiation
  2. Propagation
  3. Termination
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17
Q

What factors influence degree of polymerization?

A

vanderwalls space(molecular bond length) and free space(due to random thermal energy and rotational mvmt)

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18
Q

Methods to decrease contraction during polymerization

A
  1. add more inorganic filler
  2. add more prepolymerized particles
  3. use methylacrylate particles with HIGH molecular wieght
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19
Q

Activation and polymerization methods inculde

A
  • light activation via blue light (465nm)
  • chemical activation
  • dual curing (chem and light)
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20
Q

how long does setting reaction continue?

A

24 hours

21
Q

when is mechanical strength attained after placing composite?

A

immediately after curing the restoration

22
Q

how long does it take composite to loose capability to flow when exposed to light?

A

60-90 seconds

23
Q

Setting times for chemically activated composites range from

A

3-5min

24
Q

What do inorganic oxides provide to a composite?

A

coloration

25
Q

What properties can be improved if composites are judiciously developed?

A
  • modulus
  • strength
  • fracture toughness
  • wear resistance
  • thermal expansion
  • chemical corrosion resistance
26
Q

what size particles are mixed in micro hybrids?

A

.04-1 micrometers

27
Q

Microhybrid qualities

A

good stress and wear resistance but get dull with time

28
Q

what is cermet?

A

glasses fused with metals such as gold, silver and titanium

29
Q

what is the purpose of cermet?

A

to improve the strength of glass ionomers

30
Q

what are the properties of macrfills?

A
  • early composites
  • spherical or irregular shaped particles
  • opaque
  • low resistance to wear
31
Q

What is a hybrid composite?

A

two types of fillers blended together, has irregular shapes
-fine particles 2-4 micrometers
and 5-15%microfine particles(usually silica)

32
Q

what makes up microhybrid composites?

A

77-84%filler by weight

  • fine particles size .04-.1 micrometer blended with microfine silica
  • has irregular shapes
33
Q

what does distribution of filler particles provide

A

efficient packing so high filler loading is possible

34
Q

Hybrids and microhybrids pros and cons

A

good clinical wear resistance, mechanical properties for stress-bearing spots
Lose surface polish, becoming rough and dull

35
Q

purpose of fillers:

A
  1. reinforce resin matrix
  2. provide appropriate translucency
  3. control volume shrinkage of the composite during polymerization
36
Q

Most common monomers used are:

A

aromatic dimethacrylates
(also bisGMA and UDMA)
-high viscosity so dilutants must be added

37
Q

coupling agent

A

silane applied to inorganic particles to surface treat the fillers before being mixed with the unreacted monomers

38
Q

which composite type has the best polish and esthetics?

A

Microfilled(but has higher shrinkage)

39
Q

Which composite has the highest volume of inorganic filler?

A

Nanocomposite 78.5%

40
Q

Which composite has the lowest volume of inorganic filler?

A

Flowable-syringeable and lower modulus

disadvantage: has higher wear

41
Q

Advantages of nanocomposite

A

high polish, high strength , high modulus

42
Q

disadvantage of microfilmed composite

A

higher shrinkage

43
Q

disadvantage of flowable composite

A

higher wear

44
Q

advantages of multipurpose composite

A

high strength high modulus

45
Q

are Glass ionomers classified as composites?

A

yes

46
Q

Glass ionomer properties include

A

water based material

acid-base setting reaction

47
Q

high elastic modulus

A

more stiff

48
Q

low elastic modulus

A

less stiff, higher fracture toughness

Dental Materials (1 decks)

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